In the case of water jet surgery, a jet of physiological saline solution is directed onto a biological tissue by a suitable instrument, said tissue being completely or partially cut and/or severed. Gentle operation techniques are thus possible. The corresponding instrument has to be supplied with the treatment fluid, in particular NaCl solution, at the desired pressure and/or desired delivery volume. For this purpose, a pump unit is used in the prior art that typically has two separately driven pump pistons working in opposite directions. It is thus ensured via corresponding inlet and outlet valves that the pump pistons suck in NaCl solution and deliver this in a manner directed towards the instrument.
Such pump units are provided sterile, for example as disposable articles. The pump unit is a medical sterile product. This requires that the pump unit be produced under particular cleanliness requirements, for example in a clean room, and cleaned after assembly where appropriate. In particular, the pump unit must be sterilised following assembly. To this end, gas sterilisation methods can be used in which appropriate sterilisation gases, such as ethylene oxide, formaldehyde, peracetic acid or the like, are guided through the channels of the pump unit. However, since the pump unit is configured to convey liquids, but not to convey gases, it is a challenge to ensure that the sterilisation gas used actually reaches all relevant points of the pump unit.
A further problem with the pump units arises due to the required large range of adjustable delivery volumes. Both with quick and also in particular with very slow piston movement, a uniform, non-pulsating, continuous NaCl jet must be produced. This places particular requirements on the inlet and outlet valves of the pump unit.